1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus including the optical scanning device.
2. Description of the Related Art
An image forming apparatus such as a printer, a copier, or a facsimile machine includes an optical scanning device that forms a latent image by irradiating a photoconductor with a light beam emitted from a light source. Such image forming apparatus acquires an image by developing the latent image formed on the photoconductor into a visible image, transferring the visible image directly from the photoconductor or through an intermediate transfer body to a transfer material, and fixing the visible image onto the transfer material.
The optical scanning device includes the light source, a polygon scanner being a rotary deflector, a pre-polygon optical system installed on a path of a light beam from the light source to the polygon scanner, a scanning lens, and a reflecting mirror. These components are mounted to a base member of the optical scanning device and covered with a cover member in order to prevent deposition of dust or dirt on the component items, where the base member and the cover member together form a casing of the optical scanning device. Moreover, dust-proof glass is installed at an opening of the casing and configured to prevent the dust or dirt from entering the casing, the opening being a light path through which the light beam emitted toward the outside of the casing passes.
The polygon scanner forms a latent image by rotating a polyhedral mirror at high speed and scanning the light beam from the light source on the photoconductor. A sound generated when driving the polygon scanner such as a wind noise of the polyhedral mirror rotating at high speed possibly becomes a noise that causes discomfort to a person around the image forming apparatus such as a user thereof, when the sound is transmitted to the outside of the apparatus.
Japanese Laid-open Patent Publication No. 2005-202117 and Japanese Laid-open Patent Publication No. H06-051228 disclose an optical scanning device which absorbs a sound that can possibly become a noise by including, in the casing, a resonator with a resonance frequency corresponding to the frequency of the sound generated when the polygon scanner is driven.
As with the optical scanning device of the related art, however, there is a case where a gap allowing air to pass therethrough is formed at a joint portion between the base member and the cover member of the casing which houses therein the components including the polygon scanner and prevents dust or dirt from entering the casing. Such gap can cause the sound generated in the casing to be transmitted to the outside through air, whereby it has been unable to sufficiently suppress the leakage of the sound generated from the polygon scanner to the outside.
Therefore, there is a need to provide an optical scanning device which can further suppress transmission of a sound to the outside compared to the related art and an image forming apparatus including the optical scanning device, the sound being generated when the rotary deflector is rotationally driven.